Dispersion-corrected density functional theory calculations of the molecular binding of n-alkanes on Pd(111) and PdO(101)

Abstract

We investigated the molecular binding of n-alkanes on Pd(111) and PdO(101) using conventional density functional theory (DFT) and the dispersion-corrected DFT-D3 method. In agreement with experimental findings, DFT-D3 predicts that the n-alkane desorption energies scale linearly with the molecule chain length on both surfaces, and that n-alkanes bind more strongly on PdO(101) than on Pd(111). The desorption energies computed using DFT-D3 are slightly higher than the measured values for n-alkanes on Pd(111), though the agreement between computation and experiment is a significant improvement over conventional DFT. The measured desorption energies of n-alkanes on PdO(101) and the energies computed using DFT-D3 agree to within better than 2.5 kJ/mol (< 5%) for chain lengths up to n-butane. The DFT-D3 calculations predict that the molecule-surface dispersion energy for a given n-alkane is similar in magnitude on Pd(111) and PdO(101), and that dative bonding between the alkanes and coordinatively unsaturated Pd atoms is primarily responsible for the enhanced binding of n-alkanes on PdO(101). From analysis of the DFT-D3 results, we estimate that the strength of an alkane η(2)(H, H) interaction on PdO(101) is ~16 kJ/mol, while a single η(1) H-Pd dative bond is worth about 10 kJ/mol.

Adsorption of small hydrocarbons on rutile TiO2(110)

“…The offset for the highly active PdO(101), which efficiently oxidizes all alkanes except methane and ethane [47,48], was found to be even higher, 25 kJ/mol [74,77], and was attributed to the dative bonding interactions between the alkanes and the cus-Pd atoms of the PdO(101) surface [47,50,51,74]. The alkane length independent enhancement suggested that the molecule-surface dative bonding produces a similar contribution to the total binding energy for all the n-alkanes (C 1 to C 5 ) studied.…”

Ab Initio Calculation of Rate Constants for Molecule–Surface Reactions with Chemical Accuracy

“…However, for large chemical systems, such as those encountered in heterogeneous catalysis, where adequate models typically include several hundred atoms, the “chemical accuracy” (4 kJ mol −1 for the energy barriers, one order of magnitude for the pre‐exponential factors) required for useful predictions is not attained. The exponential scaling with the system size of both the electronic structure methods (potential energy surface) and the nuclear motion problem (vibrational partition function) limits the applicable method to density functional theory (DFT) for the potential energy surface and the harmonic approximation for the vibrations 4, 5, 6, 7, 8. Depending on the functional, energy barriers may be in error by 10–20 kJ mol −1 , and the harmonic approximation is most problematic for low‐frequency modes, which are known to make the largest contribution to the partition functions 9…”

Propane Fuel Cells: Selectivity for Partial or Complete Reaction

“…Other computed values for propane adsorption on metals include values of 33-38 kJ/mol on Pt, shown by Nykänen and Honkala [30], a value of 55 kJ/mole on Pd, shown by Antony et al [31] and 39.8-42.1 on Pd, shown by Kao and Madix [32]. Experimental values for propane adsorption on metals include a calorimetric measurement of 32 kJ/mol on a Mo film by Smutek andČerný [33], and temperature programmed desorption measurements on Pd, shown of 41.5 kJ/mol, shown by Kao and Madix [32] and 45 kJ/mol, shown by Antony et al [31]. Nykänen and Honkala [30] noted that there is considerable uncertainty in heat measurements made by temperature programmed desorption.…”